1. Technical Field
The present invention relates generally to a faraday system, and more particularly, to a system, method and program product for determining the integrity of a faraday system.
2. Related Art
Ion implantation is a standard technique for introducing conductivity altering impurities into, or doping, semiconductor wafers. A typical ion implantation process uses an energetic ion beam to introduce impurities into semiconductor wafers. As is well known, introducing the impurities at a uniform depth and dose into the wafers is important to ensure that semiconductor devices being formed operate properly.
The depth at which impurities are implanted depends in part upon an incidence angle of an ion beam relative to the crystal structure of the semiconductor. The incidence angle of an ion beam may be determined, inter alia, by measuring an ion beam density using a faraday system including a sampling faraday cup and/or a traveling faraday cup. The dose of an ion beam may be measured by a dose control faraday cup. A faraday system includes a faraday cup and its interconnecting system. As such, it is important to determine and maintain integrity of a faraday system to ensure an accurate measurement of an ion beam using the faraday system.
Efforts have been made to determine the integrity of a faraday system. According to one approach, a faraday cup is manually tested with an external current source manually attached to the faraday system in a specifically designed interconnection of the faraday cup. In another approach, a faraday cup is connected to two wires, and is measured under normal operation through each wire. A ratio between the two measurements by the two wires is used to determine the integrity of the faraday system. In still another approach, a faraday cup is connected to two lines. One of the lines is used to send out a test signal from a test circuitry to the faraday cup under normal operation and the other line is used to read back the signal which passes through a dose measurement path of the faraday cup. The integrity of the faraday system is determined by comparing a value of the read back signal with an expected value.
There are some disadvantages of the conventional approaches of determining faraday system integrity. First, they measure a faraday system with specially created interconnecting wires or cups, which makes the hardware more expensive, less reliable, and makes the measurements not sensitive to changes in the faraday system characteristics. Second, they measure a faraday system manually, which would require an ion implantation machine to be unproductive for longer periods of time while the measurements are being made, and would be susceptible to operator errors.
Based on the above, there is a need to test integrity of a faraday system automatically, without the need to create a special design for either the cup or the interconnecting wires from the cup. There is also a need to determine integrity of a faraday system when the faraday system is not in normal operation.